In order to commercialize electric and hybrid vehicles on a widespread basis the energy storage devices or batteries, which are the most expensive component of the vehicle, must operate reliably through the life of the vehicle. In a typical configuration, the batteries are formed from a stack of series connected electrochemical cells.
A common requirement for large stacks of electrochemical cells used in electric and hybrid vehicles, particularly in advanced applications such as lead acid Li-Ion or NiMH battery packs, is the need to measure individual or groups of cell voltages almost simultaneously. In practice, this means the measurements should be taken within a time window of a few milliseconds.
Conventionally, a flying capacitor method is used in Hybrid Electrical Vehicles for battery voltage measurement and monitoring. Referring to FIG. 1, a discrete battery sensor system employing a flying capacitor method is illustrated. As depicted in FIG. 1, an individual battery or cell Bat1-Batn of a battery pack is connected to a sensing capacitor Cs by turning on the respective Solid-State Relays (SSRs). Resistor Rs is added in series to sensing capacitor Cs to limit the transient charging current to a reasonable amount.
For example, if battery Bat1 is to be sensed, solid-state relays SSR#1 and SSR#2 will be turned on, the rest of the solid-state relays SSR3#-SSR#n will remain off and sensing capacitor Cs is then fully charged to voltage of battery Bat1. Solid-state relays SSR#1 and SSR#2 are switched off before solid-state relays SSR#11 and SSR#12 are switched on and analog-to-digital converter ADC then samples the scared version of the voltage stored at capacitor Cs through resistor divider including resistor R1X and resistor R2X. The converted digital signal representing the scaled battery voltage of battery Bat1 is then transferred to the controller for further system processing.
Solid-state relays SSR#13 and SSR#14 are used alternatively with solid-state relays SSR#11 and SSR#12 to correct the polarity inversion of the alternating batteries connected to the two common buses.
However, there are several disadvantages of the battery voltage sensing implementation shown in FIG. 1. First, in order to minimize the effect of the solid-state relays (SSRs) and parasitic leakages, the sensing capacitor Cs must be sufficiently large. A large sensing capacitor Cs means a larger amount of charge during sensing, or larger charging current if charging time to be kept constant. Secondly, a large charging current is undesirable and is likely to cause EMI problems in view of the unbalance in the charging path impedances. A transient current limiting resistor Rs is added to limit the charging current to a reasonable amount. However, together with the sensing capacitor Cs, the low pass characteristic inevitably slows down the system speed. Additionally, the system speed is further affected by the switches, which are implemented by the solid-state relays (SSRs). Solid-state relays (SSRs) are generally quite slow due to its working mechanism. Besides, “break-before-make” must be strictly observed in a sense (or sample) and hold system. Furthermore, every solid-state relay (SSR) needs a control signal, which makes this discrete solution not only have a high component count, but also very complicated in terms of wire routings.
Therefore, a need exists for techniques for sensing individual battery voltages of a battery pack within a relatively short time period. Furthermore, a need exists for an integrated battery sensor to be utilized in a battery voltage sensing system which reduces component count and system wire routings.
Various patent documents containing subject matter relating directly or indirectly to the field of the present disclosure include, but are not limited to, the following:
U.S. Pat. No. 5,808,469 to Kopera for “Battery monitor for electric vehicles,” Sep. 15, 1998.
U.S. Pat. No. 6,094,031 to Shimane et al. for “Battery conditioning-detecting apparatus and battery condition-detecting unit using an optical signal,” Jul. 25, 2000.
U.S. Pat. No. 6,166,549 to Ashtiani et al. for “Electronic circuit for measuring series connected electrochemical cell voltages,” Dec. 26, 2000.
U.S. Pat. No. 6,411,097 to Ashtiani et al, for “Electronic circuit for measuring series connected electrochemical cell voltages,” Jun. 25, 2002.
U.S. Pat. No. 6,472,880 to Kang for “Accurate voltage measurement system using relay isolated circuits,” Oct. 29, 2002.
U.S. Patent Publication No. 2006/0164042 to Sim for “Apparatus and method for monitoring charging/discharging capacity of battery packs,” Jul. 27, 2006.
U.S. Patent Publication No. 2007/0090802 to Seo for “Battery management system,” Apr. 26, 2007.
U.S. Patent Publication No. 2007/0096697 to Maireanu for “Battery fuel gauge circuit,” May 3, 2007.
U.S. Patent Publication No. 2007/0114973 to Miyamoto for “Battery voltage monitoring apparatus,” May 24, 2007.
The dates of the foregoing publications may correspond to any one of priority dates, filing dates, publication dates and issue dates. Listing of the above patents and patent applications in this background section is not, and shall not be construed as, an admission by the applicants or their counsel that one more publications from the above list constitutes prior art in respect of the applicants' various embodiments.